Lock-in amplifiers are traditionally devices capable of recovering and measuring a signal obtained in a noisy environment. Conventional lock-in amplifiers typically convert the phase and/or the amplitude of a measured signal to a direct current, DC, voltage signal. Nowadays, lock-in amplifiers usually directly return the digitally obtained measurement result as a digital value or discrete output signal.
A conventional lock-in amplifier can often measure the input signal with a resolution and accuracy better than that given by noise and stability of the input hardware by providing a known signal to the measured object. A problem is that the signal provided to the measured object may not be stable and vary over time.
When trying to measure and study aggregated aspects of a measurement object, a plurality of channels of one or more lock-in amplifiers may be used. The result from each channel is then combined or aggregated externally to obtain an aggregated value. Various differences in timing between the channels may result in a degraded quality of the aggregated value.
An example of such an aggregated value or values may be a resistance value of a resistor. A first channel of the lock-in amplifier may monitor the voltage over the resistor. A second channel of the lock-in amplifier may simultaneously monitor the current flowing through the resistor. An aggregated value can then be generated based on the output signals of the first and second channels of the lock-in amplifier.
A problem with conventional measurement systems is that if the measured object property, such as resistance, or the signal source providing the measured object with a signal or signals is not ideal or varies over time, the aggregated value will vary over time. In the above mentioned example of a resistor, even a small time shift may distort the result if the resistor depends on temperature and the temperature is changing. Similarly, a constant resistance may appear to vary if the signal source is varying over time. Thus, the quality of the aggregated value is reduced or degraded.
Thus, there is a need for an improved lock-in amplifier, in particular a lock-in amplifier for generating aggregated measurement values.